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  Tuesday, July 29, 2014  
   
 

 
Rip Rap
ten tidbits of information

While it may sound like gibberish to someone living in the mid-west, for those of us living in water communities it's an all too familiar word.

Riprap basically is rocks or other materials arranged to prevent erosion from water, most commonly used on shorelines. Most of us know what riprap is, we grew up climbing over it to get to the water. But, how much do we really know about riprap? Below are ten tidbits of information about riprap that may be able to help you make your decision on whether or not it is right for your property.

1. Riprap is not only for shorelines. Riprap can be used anywhere where erosion from water is or can be a problem. Typically, riprap is used on shorelines of creeks and rivers to prevent erosion caused by the movement of the water in those bodies. However, this isn't the only place you will see riprap. Another useful place to put riprap is on a steep graded hill, this can prevent weather related erosion, such as rain.

2. Riprap helps to create habitat for wildlife. The Virginia Institute for Marine Science (VIMS) recommends riprap over bulkheads because it helps to create habitat for small animals. During mean or high tide the riprap is typically covered by water making it ideal for small water creatures looking for shelter.

3. The proper installation of riprap will make all of the difference in the effectiveness of erosion control. Installation methods will vary depending on the job, but typically the installation begins with grading the embankment to a 1.5:1 ratio. Then the embankment is covered with a filter cloth, followed by the riprap. It is important that there be a buried toe at the bottom of the riprap. What this means is that a hole is dug out for riprap to be installed below the mean low water mark. Ensuring that the toe is properly laid is essential to the effectiveness of the riprap.

4. The size of the rock used in riprap is determined by the climate of the project. More protected areas don't require as large of stones as the more exposed areas. For that reason typically Class 2 rocks will be used for protection against rivers and the Bay, while Class 1 rocks will be used for creeks and backwaters. Class 2 rocks range in size from 300-500 lbs. Class 1 rocks are usually between 80-150 lbs. The reason that property on rivers and the Bay require larger, heavier stone is when there is a storm the rocks have to be sufficiently heavy to withstand the water beating on them and to stay where they are positioned. This is not often the case with creeks and backwaters, so it is not as necessary to lay the heaviest rocks.

5. Riprap actually absorbs waves coming on to your property. Seawalls and other types of erosion control can deflect waves and send them to other shoreline areas. With riprap, when a wave crashes against it the wave is dampened, or absorbed, and does not bounce back to other areas.

6. In areas with very high rates of erosion riprap can be placed in front of a seawall. The seawall works as a high level of erosion protection and the riprap in front of the seawall works to keep the dirt at the bottom of the seawall from eroding away. Additionally, this helps to absorb the waves. This type of installation is preferable in inlets and marina type settings that have serious erosion problems. This is typically installed in the most extreme cases and depends largely on the exposure and the need to absorb waves.

7. Water discharge pipes are typically surrounded with riprap. This keeps the fresh water being discharged from washing away the dirt around the pipes as it enters the tributary.

8. Riprap is often used to protect marsh grasses. This is typically installed in creeks and backwaters at a 2:1 ratio in front of the marsh grass to preserve the habitat and prevent further erosion. In cases like this it is vital that the marsh grass not be disturbed so the riprap is always placed in front of the grasses.

9. Riprap can be brought in on a barge so as not to disturb the environment leading up to the shoreline. This is often done to protect habitat in the RPA (Resource Protection Area). The RPA is a buffer of 50-100 feet (depending on the property) aimed at protecting the Chesapeake Bay and it' tributaries. A barge can be brought in when there are trees and shrubs in this protected area that prohibit equipment from getting to the shoreline. In some cases the Chesapeake Bay Act could make the use of a barge mandatory. Other instances barges are used would be to protect landscaping. In these cases the cost of the barge is evaluated in relation to how much it will cost to repair a yard (regrading, seeding and strawing a yard).

10. Riprap was one of the very first forms of erosion control. Riprap was even used on the dams in the Panama Canal, construction of which began in the early 1800s was not completed until 1914.

These ten bits of trivia help to explain the procedures involved with installing riprap and some of their advantages. To know for sure if riprap is appropriate for your shoreline it is important to contact a marine construction expert.